In the production of pressed board it is a standard practice to spread glue-coated particles of a spreadable material in at least one layer on a conveyor or the like forming a receiving surface to constitute a mat which can be carried into a press and there subjected to pressing, e.g. hot pressing, to activate the binder and produce a pressed board.
Such pressed board, also commonly referred to as particleboard, may contain cellulosic fibers, sawdust, wood particles or the like and typical glues which may be used include phenolic or resorcinol-based thermosetting adhesives.
A typical press for this purpose is a continuous steel-belt press between the belts of which the mat is fed and from which emerges a continuous body which can be cut into the individual boards.
The steel belts may move between the press platens via the intermediary of rollers or the like.
In a prior practice, the formation of the mat utilized a bin containing the glue-coated particles and a discharge roll device which metered those coated particles from the bin onto the receiving surface. Between the receiving surface and the discharge roll device, a spreading head was provided. The usual approach was to deposit the particles directly upon the spreading head and allow the spreading head to spread the particles in the form of a mat on the surface.
In practice that approach was found to yield singular regions of the mat of higher density or more compact character than other regions. The local regions of more compact character generally resulted from clumps in the spreadable material, both as a result of the agglomeration of particles because of the presence of the glue or binder, and because particles tended to hook together.
The clumps of the spreadable material resulted not only in inhomogeneity of the finished board, i.e. local regions of greater density or lesser density, but also damage to the press belts when continuous steel-belt presses were utilized. The damage could cause buckling of the relatively thin steel belts or other permanent deformation thereof. As a result, the press itself had a limited life.